Genetic analysis of the two groups of duplicated genes coding for mitochondrial malate dehydrogenase in Zea mays: Possible origin of Mdh genes by chromosome segment duplication

Summary

The results presented in this paper demonstrate that there are four mitochondrial malate dehydrogenase genes (mMdh1, mMdh2, mMdh3, and mMdh4) as was proposed by Yang et al. (1977), but with the following modification. Yang et al. (1977) postulated that mMdh1 and mMdh2 were closely linked as were mMdh3 and mMdh4. They also proposed that mMdh3 and mMdh4 arose by gene duplication from mMdh1 and mMdh2 respectively. In the modified model mMdh3 and mMdh4 are linked, but the other two genes mMdh1 and mMdh2 are unlinked. In addition, we demonstrate using reversible denaturation techniques, which mMDH isozymes are heterodimeric in structure. Hence, the origin of all the mMDH isozymes has been elucidated.

Since the number of genes in the modified mMDH model remains the same as the Yang et al. model (1977), the original nomenclature is used. We illustrate further that the three gene model proposed by Goodman et al. (1980) and accepted by their collaborators, Newton and Schwartz (1980) is not consistent with data from our genetic crosses. However, the modified version of the Yang et al. (1977) model will account for all MDH data published to date. The psossible role of chromosome segment duplication in the evolution of the MDH genes in Zea mays is discussed.